A PRELIMINARY STUDY OF THE POLLEN FLORA OF KARACHI

Abstract

Pollen morphology of 351 species from Karachi, belonging to 67 families of Angiosperms, distributed in 58 dicots and 9 monocots have been investigated by scanning electron (S.E.M.) and Light microscope (L.M.). Considerable diversity in qualitative and quantitative characters, more especially in symmetry, polarity, shape, size, apertural types and cxine ornamentation have been observed. Pollen grains are generally isopolar-apolar, rarely subisopolar and heteropolar, commonly prolate-spheroidal to oblate-spheroidal or sub-prolate to prolate rarely spheroidal. Both types of apertures viz., simple and compound are fairly common. Grains are mostly colporate, colpate and porate rarely non-aperturate ones are also observed. The number and position of apertures also varies in different taxa. In some families namely Lythraceae, Acanthaceae and Boraginaceae more distinct heterocolpate grains are also found. Besides this, some miscellaneous type of apertures have also been observed in Neuradaceae (Neurada procumbens L.), Sapindaceae (Cardiospermum helicacabum L.) and Menyanthaceae (Nymphoides cristata (Roxb.) O.Ktze), Similarly exine sculpturing is also extremely varied, ranging from almost psilate, sub-psilate, reticulate, rugulate, fossulate, foveolate, striate, scabrate, echinate to tubuliferous spinulose. Some families viz., Acanthaceae, Boraginaceae, Convolvulaceae, Polygonaceae, Liliaceae, Typhaceae and Zygophyllaceae are eurypalynous and have quite distinct pollen types. In contrast to this, some families are fairly uniform in their pollen characters, as in Rhamnaceae, Polygalaceae, and Chenopodiaceae etc.
With few problematic exceptions, pollen data supports the general classification. The relatively most primitive pollen type i.e. monosulcate (l-colpate), heteropolar, bilaterally, symmetric pollen are restricted to the most primitive subclass of dicots i.e., Magnoliidae and to the monocots. In contrast to this the highly advanced subclass Asteridae exhibit greatest arry of specialized pollen types, more especially the family Compositae.
Pollen morphology of various orders in relation to the taxonomy is separately discussed.
Pollen vectors in relation to their respective pollination types are also discussed. In the present investigations insects are the major pollen vector, 65.24 % taxa are pollinated by insects, 33.04 % taxa utilizing wind as the dispersal agent and 1.71 % taxa are pollinated by birds and other agencies (Hydrophily)